Wednesday, October 26, 2011

LROC: Extensional Fractures

Narrow fractures extend across a complex intersection of lunar surface types northeast of Mare Serenitatis, in Lacus Somniorum. LROC Narrow Angle Camera (NAC) observation M168007062L, from the period last August when the LRO spacecraft's orbit was altered to include very low passes over selected areas (resolution 25 centimeters per pixel); orbit 9893, August 15, 2011. Field of view a bit more than 550 meters wide [NASA/GSFC/Arizona State
University]

In this 0.25 m/pixel NAC frame we found narrow fractures that extend across the lunar surface, in the mare basalt of Lacus Somniorum. Narrow fractures like these are probably extensional features caused by tension stress that pulls the rocks apart in opposite directions. Similar fractures have been found before on top of wrinkle ridges.

The fractures in today's Featured Image are also associated with a small wrinkle ridge. In the LROC Wide Angel Camera (WAC) 60 meter per pixel context image below, you can see the ridge (yellow arrow) between two hills of non-mare material. The fractures are located west of the ridge (yellow box). There are a number of other wrinkle ridges in the area as well.

LROC Wide Angel Camera (WAC) Observation M150321508C (604 nm), LRO Orbit 7288, January 22, 2011, local late afternoon illumination at incidence angle 67.201° The yellow box at center bounds the fractures seen in the LROC Featured Image, released October 26, 2011. The yellow area designates a ridge possibly related to those fractures. [NASA/GSFC/Arizona State University].